Elastomeric members are used extensively in railway cars and other systems where they are subjected to loads and deformations which tend to cause wear and require frequent replacements.
In railway car systems, for example, elastomeric members are employed in primary suspension systems. A particular type of system as related to the present invention, is described in a patent, assigned to the same assignee as the present invention, entitled "Primary Suspension System for a Railway Car", U.S. Pat. No. 4,444,122, issued Apr. 26, 1984.
An example of elastomeric bumpers, used as lateral stops, is illustrated in FIG. 4 of U.S. Pat. No. 4,192,238, issued Mar. 11, 1980.
Generally, in the case of soft primary suspension systems, the elastomeric members may include openings or voids therein to achieve greater softness and flexibility. With such openings, as described in the aforementioned patent, metal plates are bonded to the elastomeric members to prevent creeping of the elastomeric material under load conditions. When these plates are used, the various parts of the side frames into which the primary system is inserted must conform to high tolerances thereby adding to the overall manufacturing cost.
Because of the bonding of the elastomeric rings to the steel plates, it was possible to operate the primary suspension system with higher stresses or larger strains for the same forces by reducing the work in an area of the rubber ring thus providing softer spring rates. Because of the voids or cut-outs providing a softer spring and the bonding providing conditions preventing the bulging of the rubber areas of contact with the metal rings, the vertical stiffness of the primary suspension system described may be reduced to one-half or less over many designs in which compressed rubber rings were used in the primary suspension elements.
While the apparatus described in the aforementioned patent has proven satisfactory, the metal plates bonded to the elastomeric material required that the surfaces of the plate be maintained within certain tolerances to match the surfaces of the journal box and side frame between which the primary suspension system including the bonded plates are generally disposed.